Refrigerating apparatus with defrost control means



March 24, 1964 l. 1.. GOULD 3,125,862

REFRIGERATING APPARATUS WITH DEFROST CONTROL MEANS Filed Sept. 22, 1961 2 Sheets-Sheet 1 w a .4 q ('l i A g m N E N E mvrmon.

' Ira L. Gould His Attorney March 24, 1964 l. L. GOULD REFRIGERATING APPARATUS WITH DEF'ROST CONTROL MEANS Filed Sept. 22, 1961 2 Shets-Sheet 2 Compressor Cycles OFF ON OFF ON OFF Temperature IN VEN TOR.

In] L. 600/0 United States Patent 3,125,862 REFRIGERATING APPARATUS WITH DEFRQST CONTROL MEANS Ira L. Gould, Hamilton Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Sept. 22, 1961, Ser. No. 139,998 Claims. (Cl. 62-156) This invention pertains to refrigerating apparatus and more particularly to means for the controlling of the defrosting of refrigerant evaporators.

Although many devices have been devised for defrosting an evaporator when there is a predetermined build up of frost thereon, none of such devices has achieved any wide spread commercial success. The deposit of frost upon a finned evaporator with forced air circulation is particularly serious because the narrow air passages be tween the fins become clogged with frost quickly, not only reducing the transfer of heat from the air to the fins so as to reduce the reduction in temperature of the air but also reducing the rate of air circulation through the evaporator to reduce the quantity of air cooled in a given time. For example, where the fins are spaced six to the inch, if frost reduces the space between the fins one half, the reduction in heat transfer in the refrigerant evaporator will be about sixteen percent. In addition, there will also be additional reduction in heat transfer of eleven percent due to the reduction of air flow for a combined reduction of about twenty-seven percent. It is therefore important that the evaporator be defrosted at such a time. However, more frequent defrosting than is necessary is wasteful since it undesirably effects the maintenance of proper refrigerating conditions. But there has always been ditliculty in finding a rapid change taking place at the time the frost becomes objectionable enough to make defrosting desirable which can be used to generate a force sufficient to operate a defrost control to initiate a defrost cycle.

It is an object of this invention to arrange a refrigerating system in such a way as to provide, coincidental to the formation of an objectionable amount of frost, a rapid reliable change capable of generating a force sufficient to operate a defrost control to initiate a defrost cycle.

It is another object of this invention to arrange a refrigerating system in such a way as to provide, coincidental to the formation of an objectionable amount of frost, a rapid reliable change in temperature sufiicient to operate a thermostatic defrost control.

It is another object of this invention to provide a combined accumulator and interchanger providing a large ahount of heat interchange at the outlet of the evaporator and to provide a defrost thermostatic control switch on the suction line on the outlet of this accumulator interchanger to initiate a defrost cycle upon a predetermined low temperature of this thermostatic control.

These and other objects are attained in the form shown in the drawings in which a cross-finned evaporator having six fins to the inch is provided with an electric defrost heater. At the outlet of the evaporator, there is provided a combined accumulator and interchanger where there is concentrated substantially all of the interchange that is desirable between the warm liquid from the condenser and the cold gas from the evaporator. A fan is provided to circulate air from the compartment to be cooled through the evaporator. The motor-compressor unit is controlled in accordance with the temperature of the air at the inlet side of the evaporator. I find that, if this accumulator interchanger arrangement provides an adequate amount of heat interchange, there is a large drop in temperature at the end of the running cycle when the evaporator becomes heavily frosted sufiiciently to 3,125,862 Patented Mar. 24, 1964 ice make defrosting desirable. According to my invention, I provide a wide differential bimetal switch upon the suction conduit adjacent the outlet of the accumulator. This wide differential type of bimetal switch operates when cooled to an abnormally low temperature to initiate a defrost cycle. This defrost cycle continues until this bimetal switch is heated sufiiciently to return to its normal refrigeration position.

The operation of the bimetal defrost switch stops the motor-compressor unit as well as the evaporator and condenser fans and energizes an electric defrost heater associated with the evaporator. The defrost heater heats the evaporator and melts the frost therefrom until the bimetal defrost switch is heated sufiiciently to reset. The resetting of the bimetal defrost switch resumes the normal control of the motor-compressor unit and fans providing normal refrigeration until the evaporator again becomes coated with frost.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a diagrammatic plan view of a refrigerating system embodying one form of my invention;

FIGURE 2 is a sectional view taken along the line 2-2 of FIGURE 1 of the suction line showing the bimetal defrost switch attached thereto;

FIGURE 3 is a wiring diagram for the system shown in FIGURE 1; and

FIGURE 4 is a temperature-time chart showing the variations in temperature of the suction line at the bimetal defrost switch location during running and idle periods.

Referring now to the drawings and more particularly to FIGURE 1, there is shown diagrammatically a sealed motor-compressor unit 20 which compresses refrigerant and forwards the compressed refrigerant through a conduit 2?; to the condenser 24 where the compressed refrigerant is liquefied and forwarded through a filter drier 25 to a capillary supply conduit and restrictor 26. The capillary tube supply conduit 26 has a heat transfer portion 32 which extends in three lengthwise sections bonded in heat transfer relation to the accumulator 30 and adjacent portions of the suction conduit 28 and the outlet conduit 38 so as to provide a combined accumulator and interchanger. The accumulator 30 is about 4 inch in diameter and about 9 /2 inches long. The heat transfer portion 32 is about 40 inches long. The capillary tube supply conduit 26 connects to the inlet 34 of the evaporator 36. The evaporator 36 is of the cross fin and tube type having about six fins per inch. The outlet conduit 38 of the evaporator 36 is connected to the inlet of the accumulator 30. The suction conduit 28 is connected to the outlet of accumulator 30. A centrifugal fan 40 driven by an electric motor 42 is provided with an inlet shroud 44 connecting the outlet side of the evaporator 36 for drawing air from the inlet side through the fins thereof. The centrifugal fan 40 discharges through its outlet 46 into a compartment 48 to be kept cold. If desired, this compartment 48 may be kept at freezing temperatures. The air from the compartment 48 circulates to the inlet side of the evaporator 36. In front of the inlet side of the evaporator 36 is a thermostat bulb 50 operatively connected to the thermostat switch 52 which controls the operation of the motor-compressor unit 20 and the fan motors 42 and 54 to coincidentally accumulate frost upon the evaporator 36. The fan motor 54 operates the fan 56 which circulates outside air in heat transfer with the condenser 24. If desired, both fans 40 and 56 may be driven by a single motor instead of separate motors as shown.

In the refrigeration circuit according to my invention, the accumulator 30 is of copper tubing about 4 inch 0.1). and about 8 inches long. The capillary tube supply conduit 26 is also of copper and has internal and external diameters of about 0.031 inch and 0.083 inch. The supply conduit 26 is bonded lengthwise to the side of the suction conduit 28 for a distance of about 9 inches between the defrost switch 58 and the accumulator 30. The conduit 26 continues by being bonded lengthwise to the same side of the accumulator 30 in counterflow heat transfer and then is looped back and bonded lengthwise along the diametrically opposite side midway between the top and bottom of the accumulator. The supply conduit continues to a looped portion bonded to the side and bottom of about 2% inches of the suction conduit 28 adjacent the accumulator 30 and is further bonded lengthwise to the bottom of the accumulator 30 and about 3 inches of the bottom of the outlet conduit 38 adjacent the accumulator 30. This provides the heat transfer portion 32 with a total length of about 40 inches of the conduit 26 in heat transfer with the accumulator 30 and the adjacent portions of the conduits 28 and 38.

Under conditions of normal operation, the evaporator 36 coincidentally accumulates frost since the temperature at the outlet of the evaporator 36 is about 2 F. The heat supplied by the heat transfer portion 32 is sufficient to normally raise this temperature to about 50 to 55 F. at the location of the switch 58 when the environment temperature is 70 F. This is between about seventy ercent and seventy-eight percent of the difference between the 70 F. room temperature and the evaporator outlet temperature of 2 F. The heat supplied by the heat transfer portion 32 is sufficient to raise this temperature to about 70 to 75 F. at the location of the switch 58 when the environment temperature is 110 F. This is between about sixty-three percent and sixty-eight percent of the difference between the room temperature of 110 F. and the outlet temperature of 2 F. The values in between environment temperatures of 70 F. and 110 F. can be expected to be proportional.

I have found that with this accumulator interchanger 30, 32, when the thermostat 52 is set to close at 155 F. and to open at 4.5 F., there is a considerable difference in the temperature of the suction line near the outlet of the accumulator 30. When the evaporator 36 is substantially free of frost, the temperature of the suction line 28 near the outlet of the accumulator, during the running cycle of the motor-compressor unit 20, varies between about 40 F. and 25 F. (see FIGURE 4). Under such circumstances, the running cycles are relatively short. However, as frost builds up on the evaporator 36, the rate of heat transfer between it and the air becomes less and the quantity of air or the rate of air circulation through the evaporator 36 also becomes less. Under such circumstances, the running cycles become longer and the temperature of the suction conduit 28 at the outlet of the accumulator 30 falls a greater amount. As more and more frost accumulates, the temperature of this point on the section 28 near the outlet of the accumulator 3t) falls more rapidly and also extends to a lower temperature. I find that, when the frost accumulates in the evaporator 36 to an extent in which about half of the space between the fins is filled with frost, the temperature will fall rapidly below F. When this amount is reached, it is desirable to defrost the evaporator 36.

Therefore, according to my invention, upon the suction line 28 about inches beyond the outlet of the accumulator 30 adjacent the beginning of the interchange between the conduits 26 and 28, I provide a double throw disk-type snap-acting defrost switch 58 having a portion 6t) shaped to fit the suction line 28. This portion 60 is held against the suction line 28 by a spring clip 62.

This double throw bimetal switch 58 is set to move from the normal refrigeration position shown in FIGURE 3 to a position closing the defrost heatercircuit if its temperature is lowered below -1 F. During the defrost period, this switch 58 is warmed and it is set to move from the defrost position to the normal refrigeration position when the temperature rises to 81.2 F.

As shown in FIGURE 4, the temperature at the location of this switch 58 during a running cycle with considerable frost on the coil is indicated by the portion of the graph bearing the reference character 64. The temperature of this location on the suction line 28 at the beginning of the running cycle is indicated by the line 66 extending to a temperature of +5 F. This is due to the refrigeration produced at the beginning of the cycle by evaporating liquid refrigerant in the accumulator 30. This liquid refrigerant in accumulator 30 is rapidly exhausted and the temperature at the defrost thermostat 58 then rises rapidly as indicated by the line 68 to about 43 F. During the running period, the temperature will gradually be reduced as indicated by the line 64 to about 10 F. at the end of the running cycle. At the beginning of the idle period, there will be a small flow of warm liquid refrigerant from the condenser toward the evaporator while the temperature of the gas suction line rises rapidly. This has the effect of providing a rapid rise as indicated by the line '70 at the defrost switch 58 up to a temperature of about 45 F. This rise is also assisted by heat transmitted by conduction through the supply and return conduits 26 and 28 extending from the warm condenser 24 and the warm motor-compressor unit 20. The cold air in the compartment 48 during the idle period removes heat from the defrost thermostat 58, thereby causing it to be cooled as indicated by the curve 72.

Because of the frosted condition of the evaporator, the temperature at the thermostat 58 at the start of the next running cycle will drop rapidly as indicated by the line 74 to about 0 F. due to the evaporation of refrigerant in the accumulator 30. Thereafter, the temperature at the thermostat 58 will rise rapidly as indicated by the line '76 and, thereafter, will gradually fall as indicated by the curved line 78. As indicated by this line 78 in FIG- URE 4, during this running cycle, the temperature falls to about 4 F. at the thermostat 58. This is SUfilClGIlt to trip the thermostat 58 from its normal concave upward position for refrigeration as shown in FIGURE 3 to the lower concave downward position in which the contacts 80 and 82 are bridged by the bimetal snap-acting disk 84. When its temperature reaches a -1 F., the motorcompressor unit 20 and both fan motors 42 and 54 are deenergized. The defrost heater 86 is energized to rapidly heat the evaporator 36 so as to rapidly remove the frost therefrom. The temperature at the thermostat 58 also rises rapidly as indicated by the line 88 until a temperature of about 94 F. is reached. This is well above the tripping point 81.2 of the thermostat 58 and causes this thermostat 58 to move from the concave downward defrost position back to the concave upward refrigerating position shown in FIGURE 3. This terminates the defrost period and restarts the motor-compressor unit 20 and the fan motors 42 and 54.

As indicated by the curve 90, the temperature drops rapidly at first and, when the temperature of 34 F. is reached at the defrost switch 58, the thermostat switch 52 is opened to stop the motor-compressor unit 20 and the fan motors 42 and 54. This causes a rise in temperature as indicated by the line 92 until a temperature of 62 F. is reached; thereafter, the temperature at the thermostat 58 falls as indicated by the curve 94. When the temperature reaches about 30 F., the thermostat 52 will reclose the refrigerating circuit, thereby causing temperature to fall as indicated by the line 96 to a temperature of about 4 F. due to the brief evaporation of liquid in the accumulator 30. After this, the temperature will rise rapidly as indicated by the line 98 to a temperature of about 38 F. and then fall as indicated by the curve 121 to a tempertaure of 34 F. Cycles will continue in this manner until the frost begins to build up in substantial amounts upon the evaporator 36. The temperature at the thermostat 58, however, will always remain above a 1 F. until the evaporator 36 becomes sulficiently coated with frost to make defrosting desirable.

If it should be desired that defrosting should normally be made once a day during such times at which a refrigerator will not be in active use, there may be connected to the circuit a double throw time controlled switch 123 having one terminal connected to the supply conductor 125 and, during normal refrigeration, connecting with the contact 127 in turn connecting with the motor-compressor unit 20 through the switch 58 or for defrosting connecting with the contact 129 in turn connecting with the defrost heater 86. A suitable time control clock mechanism 131 may be provided to operate the switch 123 out of engagement with the contact 127 and into engagement with the contact 129 during the period at which it is desired to energize the heater 86 to defrost the evaporator 36 at the desired time each day. However, this timed once a day defrosting may be omitted, if not desired.

While the embodiment of the present invention, as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A refrigerating system including liquefying means and evaporating means, supply and return conduit means having a portion in heat interchanging relation operatively connecting said liquefying and evaporating means, means for operating said liquefying means to coincidentally accumulate frost upon the evaporating means, means for defrosting said evaporating means, and temperature responsive means responsive to the temperature of an intermediate portion of the return conduit means located between said portion in heat interchanging relation and said liquefying means for initiating the functioning of said defrosting means.

2. A refrigerating system including liquefying means and evaporating means having a refrigerant outlet and inlet, an accumulator connected to the outlet of said evaporating means, supply conduit means extending from said liquefying means in heat transfer with said accumulator and connecting with the inlet of said evaporating, suction conduit means extending from said accumulator to said liquefying means, means for operating said liquefying means to coincidentally accumulate frost upon the evaporating means, means for defrosting said evaporating means, and temperature responsive means responsive to the temperature of said suction conduit means for initiating the functioning of said defrosting means.

3. A refrigerating system including liquefying means and evaporating means having a refrigerant outlet and inlet, an accumulator connected to the outlet of said evaporating means, supply conduit means extending from said liquefying means in heat transfer with said accumulator and connecting with the inlet of said evaporating means, suction conduit means extending from said accumulator to said liquefying means, having a portion in heat transfer with said supply conduit means, means for operating said liquefying means to coincidentally accumulate frost upon the evaporating means, means for defrosting said evaporating means, and temperature responsive means responsive to a predetermined low temperature of a portion of said suction conduit means adjacent said accumulator for initiating the functioning of said defrosting means.

4. A refrigerating system including liquefying means and evaporating means, means for returning refrigerant from said evaporating means to said liquefying means comprising an accumulator connected to the evaporating means and a suction conduit extending from said accumulator to said liquefying means, means for supplying liquid refrigerant from said liquefying means to said evaporating means comprising a supply conduit means, means for providing substantially the entire heat transfer between said liquid refrigerant and said returning refrigerant in direct association with said accumulator consisting of an intermediate portion of said supply conduit means extending in heat transfer relation with said accumulator, means for operating said liquefying means to coincidentally accumulate frost upon the evaporating means, means for defrosting said evaporating means, and temperature responsive means responsive to the temperature of said suction conduit means for initiating the functioning of said defrosting means.

5. A refrigerating system including liquefying means and evaporating means, means for returning refrigerant from said evaporating means to said liquefying means comprising an accumulator connected to the evaporating means and a suction conduit extending from said accumulator to said liquefying means, means for supplying liquid refrigerant from said liquefying means to said evaporating means comprising a supply conduit means, means for providing substantially the entire heat transfer between said liquid refrigerant and said returning refrigerant in direct association with said accumulator consisting of an intermediate portion of said supply conduit means extending in heat transfer relation with said accumulator, means for operating said liquefying means to coincidentally accumulate frost upon the evaporating means, means for defrosting said evaporating means, and temperature responsive means responsive to the temperature of the initial portion of said suction conduit means adjacent said accumulator for initiating the functioning of said defrosting means.

References Cited in the file of this patent UNITED STATES PATENTS 1,912,841 Haymond June 6, 1933 2,459,173 McCloy Jan. 18, 1949 2,647,189 De Puy July 28, 1953 2,885,513 Judd May 5, 1959 2,991,630 Wurtz July 11, 1961 3,010,288 Jacobs Nov. 28, 1961 3,022,639 Brown et al. Feb. 27, 1962 3,023,589 Jacobs Mar. 6, 1962 

1. A REFRIGERATING SYSTEM INCLUDING LIQUEFYING MEANS AND EVAPORATING MEANS, SUPPLY AND RETURN CONDUIT MEANS HAVING A PORTION IN HEAT INTERCHANGING RELATION OPERATIVELY CONNECTING SAID LIQUEFYING AND EVAPORATING MEANS, MEANS FOR OPERATING SAID LIQUEFYING MEANS TO COINCIDENTALLY ACCUMULATE FROST UPON THE EVAPORATING MEANS, MEANS FOR DEFROSTING SAID EVAPORATING MEANS, AND TEMPERATURE RESPONSIVE MEANS RESPONSIVE TO THE TEMPERATURE OF AN INTERMEDIATE PORTION OF THE RETURN CONDUIT MEANS LOCATED BETWEEN SAID PORTION IN HEAT INTERCHANGING RELATION AND SAID LIQUEFYING MEANS FOR INITIATING THE FUNCTIONING OF SAID DEFROSTING MEANS. 